An oil passage provided in an internal combustion engine is classed as an oil passage adapted for lubrication and cooling, an oil passage designed for drive, and the like. The former passage supplies engine oil from an oil pan to lubricated sections by an oil pump drawing the engine oil upward from the oil pan. The latter oil passage supplies the engine oil as drive pressure to a variable valve timing actuator. The actuator is disposed on one side of a camshaft.
The oil passage designed for drive is communicated to a main oil gallery of the engine in order to permit the engine oil in the main gallery to be guided into the actuator, thereby adjusting valve timing toward spark advance or delay.
One such example of an oil passage is disclosed in published Japanese Patent Application Laid-Open No. 5-288022. In a device for supplying working oil to a variable valve timing mechanism for an engine as disclosed therein, the working oil is supplied to the mechanism through an oil passage in a camshaft from one of the journal portions of the camshaft, which journal portion is positioned between a journal portion at an end of the camshaft and a central portion of the camshaft in an axial direction thereof. The device supplies the working oil to the variable valve timing mechanism in a stable manner, and the mechanism thereby provides improved response.
Another example of the oil passage is disclosed in published Japanese Patent Application Laid-Open No. 6-159020. In a valve timing adjuster as disclosed therein, even when communication between a source of oil pressure and first and second annular grooves is cut off, oil from a journal-lubricating passage permits lubrication between a cam journal portion and a bearing portion to be always retained in a good condition. In addition, the oil leaking from the journal-lubricating passage is supplied substantially evenly to the first and second annular grooves. As a result, the valve timing adjuster is always actuated in an invariable manner.
A further example of the oil passage is disclosed in published Japanese Patent Application Laid-Open No. 6-317113. In a valve-driving mechanism for an engine as disclosed therein, a cylinder head is formed with a head-side hydraulic passage for communicating an opening of an in-shaft hydraulic passage with a block-side hydraulic passage. The block-side hydraulic passage is formed in a cylinder block. In addition, there is formed a lubricating oil passage that is communicated to a journal portion. The lubricating oil passage is branched off from the head-side hydraulic passage. Further, the head-side hydraulic passage has a changeover valve provided at the branch portion thereof, but displaced toward the journal portion. The changeover valve interrupts a supply of hydraulic pressure. As a result, there is provided improved response to switching of valve timing.
A yet further example of the oil passage is disclosed in published Japanese Patent Application Laid-Open No. 7-166831. In a camshaft-lubricating device for an internal combustion engine as disclosed therein, there are provided a lubricating oil supply hole and a branch passage in order to reliably lubricate respective camshaft bearing surfaces, thereby preventing seizing thereof. The lubricating oil supply hole is communicated to a main oil gallery in a cylinder head. In addition, the supply hole is open to a surface where a camshaft bearing portion and a cam bracket are jointed together. The branch passage is formed along the joint surface between the camshaft bearing portion and the cam bracket. In addition, a distal end of the branch passage is bifurcated so as to be open to the opposite camshaft bearing surfaces, with a peripheral groove being sandwiched therebetween. Further, the branch passage is communicated to the lubricating oil supply hole. The camshaft bearing surfaces are two surfaces divided by the peripheral groove that is formed in a cam journal.
Still another example of the oil passage is disclosed in published Japanese Patent Application Laid-Open No. 9-170415. In an oil passage structure for an internal combustion engine as disclosed therein, an oil passage is laid out compactly in a small space without any changes in position and size of a cam cap bolt.
A yet further example of the oil passage is disclosed in published Japanese Patent Application Laid-Out No. 9-170416. In an oil passage structure for an internal combustion engine as disclosed therein, one oil passage designed for control and another designed for lubrication are rationally arranged in order to form a compact internal combustion engine having a reduced transverse width and a reduced entire length.
Another example of the oil passage is disclosed in published Japanese Patent Application Laid-Open No. 9-222008. In an engine having a lubrication device provided therein as disclosed therein, oil is supplied to first and second tensioners branched off from a main gallery, independently of a system of oil supply to a valve-driving mechanism. There is provided a reduced length of oil supply, which reaches a bearing portion of the second tensioner. In particular, when the engine is started up, there is provided improved response of oil supply to the bearing portions of the second tensioner. In addition, a simplified path of oil supply is provided.
A further example of the oil passage is disclosed in published Japanese Patent Application Laid-Open No. 9-280014. In a valve-driving camshaft structure as disclosed therein, a camshaft has an oil hole provided therein along the axis of the camshaft at a portion extending between a distal end of a bolt and a threaded portion of the bolt. An elongated bore portion is provided at the distal end of the bolt. The elongated bore portion corresponds to the above oil hole. A space between the elongated bore portion and an inner wall of the oil hole of the camshaft is formed as one oil passage. In addition, an intermediate hole provided at a central portion of the bolt along the axis of the bolt is formed as another oil passage. Thus, a compact structure with improved strength is realized.
A still further example of the oil passage is disclosed in published Japanese Patent Application Laid-Open No. 10-8987. In a chain cover structure for a four-cycle engine as disclosed therein, the entire chain cover is formed as a member separate from a cylinder head. The chain cover is formed integrally with a mounting portion, on which an oil supply portion for a valve timing variable device is mounted. As a result, improved operability is obtained when a chain guide and the like is built on the chain cover.
A yet further example of the oil passage is disclosed in published Japanese Patent Application Laid-Open No. 10-8988. In a four-cycle engine having a variable valve timing device as disclosed therein, the variable valve timing device is disposed on one camshaft for changing phase angle between a cam sprocket and the other camshaft in response to a variation in hydraulic pressure that acts on an oil housing body through an oil control solenoid valve. The oil housing body attached to the aforesaid one camshaft is positioned outward in the direction of the camshaft from a primary sprocket of the other camshaft. One of intake-side valve timing and exhaust-side valve timing is independently controllable. A spacing between the respective axes of intake and exhaust camshafts is reduced, thereby providing a compact cylinder head as well as a compact combustion chamber.
Still another example of the oil passage is disclosed in published Japanese Patent Application Laid-Open No. 10-121918. In a valve characteristic control device for an internal combustion engine as disclosed therein, a restricting means is provided around a discharge hole of a drain passage for restricting a mixed inflow of oil other than oil to be discharged into a deoiling portion. As a result, a valve characteristic variation mechanism ensures enhanced actuation response.
FIGS. 34 and 35 illustrate a conventional oil passage for the engine, in which an internal combustion engine 402 has a variable valve timing (also referred to as "VVT") actuator 456 positioned on one side of an intake-side camshaft 416. Referring to FIG. 35, a machined oil passage 458 is shown provided in either cylinder head 406 or cylinder block 404 for supplying oil to the actuator 456.
When a VVT-dedicated oil passage as previously mentioned is provided in the cylinder head or block of the existing engine, which is not designed for the above actuator, then related facilities in very large casting facilities and machining facilities must be changed. Such changes in facilities bring about an inconvenience of associated high costs, which is disadvantageous from an economic viewpoint.
FIGS. 36 and 37 disclose an optimum engine for description of problems to be solved. A second oil pipe for supplying the oil to the actuator is mounted on a cam housing 468 at a position above the intake-side camshaft between two cam housing bolts. As shown in FIG. 37, a breather chamber 478 is formed inside a cylinder head cover 410. The cylinder head cover 410 has an inwardly protruding relief portion 476 formed therein so as to avoid the position where the second oil pipe 470 is mounted on the cam housing 468. As a result, as seen from FIG. 37, the breather chamber 478 has a passage of small width "W1", and an oil mist flows through such a narrow passage at an increased velocity of flow. This causes another inconvenience that the oil-separating performance of the breather chamber is degraded, which is disadvantageous in view of practical use.
A further inconvenience arises from a construction in which the second oil pipe is positioned over a timing chain extending between intake-side and exhaust-side cam sprockets. More specifically, when the timing chain is swung, then there is a likelihood that the timing chain bumps against the second oil pipe, and that the second oil pipe is thereby damaged.
Further, when the second oil pipe is formed by two oil pipes different in length in which one is an advance-side second oil pipe while the other is a delay-side second oil pipe, then the longer pipe is employed as the advance-side second oil pipe. The advance-side second oil pipe uses the rear side of an oil groove that is provided in the camshaft.
When ignition timing is advanced, the variable valve timing actuator requires greater energy than when the ignition timing is delayed. As a result, the advance-side second oil pipe suffers from an increased loss of pressure when the ignition timing is advanced. This causes another inconvenience that the actuator is actuated for an increased period of time, which is disadvantageous in view of practical use.
In order to obviate or minimize the above inconveniences, the present invention provides an oil passage for an internal combustion engine, having a cylinder head attached to the top of a cylinder block and an oil pan fitted to the bottom of the cylinder block, the oil passage supplying engine oil to lubricated sections by an oil pump pumping the engine oil up from the oil pan, the oil passage using the engine oil as drive pressure on a variable valve timing actuator, the actuator being disposed on one side of a camshaft, comprising: a timing chain entrained around a crank sprocket and a cam sprocket, the crank sprocket being mounted on a crankshaft of the engine, the cam sprocket being positioned on the camshaft; and, a timing case disposed on one side of the engine for enclosing the timing chain; wherein the oil passage for supplying the engine oil to the actuator is connected at an upstream side thereof to a downstream side of the oil pump, while a downstream side of the oil passage is positioned inside the timing case and around the cam sprocket.
Pursuant to the above-described invention, the upstream side of the oil passage is connected to the downstream side of the oil pump, while the downstream side of the oil passage is located inside the timing case and around the cam sprocket. The oil passage is not provided in components produced by large-scaled facilities such as the cylinder block or head, but is provided using components fabricated by small-scaled facilities or small-sized components. Thus, manufacturing facilities are changed at small costs when an existing internal combustion engine is utilized so as to meet technical specifications of the actuator. As a result, a low cost internal combustion engine designed for the actuator is realized.